The present invention relates to door closers or door checks in general, and more particularly to improvements in door checks of the type wherein a shaft is caused to rotate in response to pivoting of a door panel to open or closed position under the action of an arm one end portion of which is non-rotatably affixed to the shaft and the other end portion of which is slidable along a guide mounted on the door frame if the shaft is mounted on the panel or vice versa.
In door checks of the above outlined character, the panel is pivoted to open position against the opposition of resilient means serving to return the panel to the closed position as soon as a person, a vehicle or a holding device ceases to apply a force which causes the panel to move toward its fully open position or to dwell in the open or partly open position. Moreover, such door checks comprise suitable dampers which ensure a more or less gradual closing of the panel, i.e., the damper prevents the panel from slamming against the frame of a door under the action of the resilient means. The just described door checks are preferred under circumstances when the appearance is important and/or when the available space does not allow for the installation of other types of door checks, especially those wherein the shaft is rotated by a linkage normally including a first link which is non-rotatably connected to the shaft and a second link which is articulately connected to the first link and to a fixed pivot member on the panel or on the door frame. However, the presently known door checks of the type wherein the shaft is connected with an arm which is slidable along a guide rail or the like exhibit a number of serious drawbacks so that their popularity is rather limited. One of the most serious drawbacks of such door checks is that the closing force is often a small fraction of the closing force of door checks which employ a linkage between the rotatable spring-biased shaft and the door frame or door panel. The difference between the closing forces of the two types of door checks can be as high as 60 percent. An undesirable consequence of the relatively small closing force of door checks with a single arm is that the magnitude of the force which is required to pivot a door panel from its closed position increases during the initial stage of pivoting through an undesirably large angle (up to and even in excess of 60 degrees). This is in contrast with the door checks wherein the shaft is connected to a linkage and the force with which the panel must be pivoted from open position decreases from a maximum value to a much lower value upon completion of an angular movement through a few degrees and thereupon decreases gradually to reach a constant value (which is much smaller than the maximum value) not later than when the panel has been caused to pivot through an angle of approximately 50 degrees.
It has been found that presently known door checks wherein the shaft is connected with a single arm offer a very pronounced resistance to movement of the door panel from its closed position through an excessive angle which causes discomfort to the person attempting to move the panel to its open position, even to a person who is accustomed to encounter a rather pronounced resistance to such movement but only during a small initial stage. This is the reason for the lack of popularity of presently known single-arm type door checks in spite of the fact that their appearance is much more pleasing to the eye than that of the door checks wherein the shaft is connected with several links and none of the links are slidable along a guide rail or the like. As a rule, door checks with a single arm are presently used only on doors wherein the required closing force is small or negligible.